1. Field of the Invention
This invention relates to blade to disk blade retention in turbomachinery and, more particularly, to boltless blade retainers particularly useful for turbines.
2. Description of Related Art
Turbomachinery blades are typically mounted by their dovetail roots into correspondingly contoured dovetail slots for radial retention during engine operation. Axial restraint within these slots have been in the past by bolts and presently by boltless assemblies using single piece split retaining rings which engage radially inward opened hooks disposed on the disk posts between the blade roots. Conventional split retaining rings are made of a spring metallic material so that the ring can be closed with a tool to provide a smaller diameter that allows it to be aligned radially inward of the hook openings and then be released to spring radially outward into the slots of the hooks thereby axially restraining the blades. Such assemblies, though used on fan and compressor blades, are not known, by the inventors, to be used in the low pressure turbine section for which the present invention was designed but not limited to.
The problem with applying such a retainer to the turbine section of an engine is that the operating temperature of the turbine blades and disk varies greatly over the engine operational envelope and the heating and cooling cycles can cause the ring to relax and fall out of contact with some or all the hooks and perhaps even disengage itself fully from its retaining position. Therefore, conventional low pressure turbine blade axial restraint is provided by many complicated multi-element types of assemblies including bolts, multiple interlocking retaining rings, and clips having bendable tabs. One such assembly having a clip with a bendable tab is shown in U.S. Pat. No. 3,653,781 entitled "Turbomachinery Blade Retainer", by James Lee Cooper, issued on Dec. 18, 1972, and assigned to the present assignee. All of these systems are characterized by complicated assemblies and assembly procedures and multiple parts that often reduce the strength of the disk and blade retainer such as in the case of bolted assemblies.
The present invention was developed to provide advantages of low weight, uncomplicated, and highly reliable single piece retaining rings and alternatively retaining rings with a very small number of pieces for use in LPT turbine blade to disk axial restraining assemblies.